It is generally accepted that normal aging and senescence are influenced by both genetic and environmental effects, but there is a dearth of available information relating to their specific nature and relative magnitude. The primary objective of the proposed research is to identify and evaluate the major genetic and environmental sources of variation and interactions among them with respect to normal life span in populations of Drosophila melanogaster. By means of laboratory experiments, largely employing classical methods of quantitatives genetics, a large body of basic data will be obtained. These experiments will include studies of the distribution of longevity, the estimation of genetic and environmental variance components, the estimation of phenotypic, genetic and environmental correlations between longevity and other quantitative traits and the effects of mass selection, inbreeding, parental age and Lansing effects. Analysis and interpretation of the data obtained from these experiments is expected to contribute to the understanding of aging processes in man.